Investigation on micro-bubble flotation and coagulation for the treatment of anaerobically treated palm oil mill effluent (POME)

• Micro-bubbles and coagulation were used for post treatment of POME.
• Optimum bubbling time was 12.5 min, removing 53.7% of chemical oxygen demand.
• Micro-bubble flotation alone was insufficient to achieve discharge limit.
• Micro-bubble flotation with PAC dosage of 2 mg/L was needed to meet discharge limit.

The rapid expansion of the palm oil industry has led to the generation of large volumes of POME in Malaysia. Most conventional aerobic processes for post-treatment of POME are unable to consistently meet environmental discharge standard due to the susceptibility of microorganisms to variable climatic conditions. The main aim of this study was to investigate the potential use of micro-bubbles generated from a venturi tube and the coagulation with polyaluminium chloride (PAC) as a post-treatment method for POME. The micro-bubbles generated from the venturi are capable of removing 57.3% of total suspended solid (TSS) and 74.5% of oil and grease (O&G) and improve the chemical oxygen demand (COD) by 53.7% and biochemical oxygen demand (BOD) by 77.0% with a bubbling time of 12.5 min and a flow rate of 19.8 L/min. However, a single-stage micro-bubble flotation is unable to treat the POME to meet environmental discharge standard. Thus, different PAC coagulant dosage are investigated and the optimum dosage is 2 g/L resulting in at least 93% of COD removal.